2020 Instruction 1040 (irs.gov)
If you were covered by a retirement plan (qualified pension, profit-sharing (including 401(k)), annuity, SEP, SIMPLE, etc.) at work or through self-employment, your IRA deduction may be reduced or eliminated. But you can still make contributions to an IRA even if you can't deduct them. In any case, the income earned on your IRA contributions isn't taxed until it is paid to you
IRA Deduction
If you made any nondeductible contributions to a traditional individual retirement arrangement (IRA) for 2020, you must report them on Form 8606.